Adamantane, tricyclo-[3.3.1.1.3,7]decane, is perhaps the simplest of the group of hydrocarbons called diamondoids. It is a polycyclic alkane with the structure of three fused cyclohexane rings. The ten carbon atoms which define the framework structure of adamantane are arranged in an essentially strainless manner. Four of these carbon atoms, the bridgehead carbons, are tetrahedrally disposed about the center of the molecule. The other six (methylene carbons) are octahedrally disposed. Adamantane has been found to be a useful building block in the synthesis of a broad range of organic compounds. U.S. Pat. Nos. 5,019,660 to Chapman and Whitehurst and 5,053,434 to Chapman teach diamondoid compounds which bond through the methylene positions of various diamondoid compounds, including adamantane. For a survey of the chemistry of diamondoid molecules, see Adamantane, The Chemistry of Diamond Molecules, Raymond C. Fort, Marcel Dekker, New York, 1976.
Many hydrocarbonaceous mineral streams contain some small proportion of diamondoid compounds, typically less than about 0.1 or even 0.01% by weight. These high boiling, saturated, three-dimensional polycyclic organics are illustrated by adamantane, diamantane, triamantane and various side chain substituted homologues, particularly the methyl derivatives. These compounds have high melting points and high vapor pressures for their molecular weights and have recently been found to cause problems during production and refining of hydrocarbonaceous minerals, particularly natural gas, by condensing out and solidifying, thereby clogging pipes and other pieces of equipment.
The problem of deposition and plugging by solid diamondoids in natural gas production equipment has been successfully addressed by a controlled solvent injection process. U.S. Pat. No. 4,952,748 to Alexander and Knight teaches the process for extracting diamondoid compounds from a hydrocarbon gas stream by contacting the diamondoid-laden hydrocarbon gas with a suitable solvent to preferentially dissolve the diamondoid compounds into the solvent.
Separation of the diamondoid compounds from the diamondoid-enriched solvent is complicated by the fact that numerous diamondoid compounds boil in a narrow range of temperatures surrounding the boiling range of the most preferred solvents. U.S. Pat. Nos. 4,952,747, 4,952,749, and 4,982,049 to Alexander et al. teach various methods of concentrating diamondoid compounds in the solvent for, among other reasons, recycling the lean solvent fraction for reuse. Each of these processes produces an enriched solvent stream containing a mixture of diamondoid compounds. In addition, U.S. Pat. No. 5,120,899 to Chen and Wentzek teaches a particularly useful method for sorbing and isolating diamondoid fractions.
Hydrocracking is a well known process. The catalysts used for hydrocracking comprise an acid component and a hydrogenation component. Most commonly, the hydrogenation component will be a noble metal such as platinum or palladium or non-noble metal such as nickel, molybdenum or tungsten or a combination of these metals. The acidic cracking component may be an amorphous material such as an acidic clay or amorphous silica-alumina or, alternatively, a zeolite. Large pore zeolites such as zeolites X or Y have been conventionally used for this purpose because the principal components of the feedstocks (gas oils, coker bottoms, reduced crudes, recycle oils, FCC bottoms) are higher molecular weight, relatively large hydrocarbons which will not enter the internal pore structure of the smaller pore zeolites and therefore will not undergo conversion.
U.S. Pat. No. 5,080,776 to Partridge et al. teaches a two-stage method for converting diamondoid-containing wash oils, and more specifically diamondoid molecules, to gasoline comprising a first hydrocracking stage and a second reforming stage.
The above-listed U.S. Patents are incorporated by reference as if set forth at length herein for the details of recovering and concentrating diamondoid compounds.